need help getting good bball action shots

Hi all
I'm new here but hoping for some expert advice!!
I've gotten in over my head as the league photographer for my daughters bball team. I have a cannon rebel XT with an 18-55 mm and a 75-300 lens. With the poor lighting in the elementary school gyms, my shots are blurry no matter what I try. Should I purchase a more powerful flash? What else can I do??
Thanks for you help!

Use the 75-300 at 75 or the 18-55 at 55; whichever has the lowest f-stop . Find a spot on the floor that has the best light and get as close as you can to that spot. Shoot whatever happens there and forget the rest of the court. - TF